Aeolian Systems Research Articles

On Optimal Functioning of the Aeolian Electro-Power Systems

The paper approaches the possibility of power functioning of the Aeolian systems. Power Aeolian systems, due to high inertia moments and rapid variation in time of the wind speed cannot constantly function on the maximum power point. Therefore it must be considered the matter of determining the optimal functioning speed of the Aeolian device on the basis of evaluating the momentary wind speed in order to get maximum of electric power. The calculation is based upon an original mathematical model for the wind turbine TV and an experimental direct follow of the wind speed in time. Actually, it is presented the way of loading the generator according to the wind speed.etc.

Luminescence-based dune chronologies in southern Africa: Analysis and interpretation of dune database records across the subcontinent

Over 600 luminescence ages have to date been published from southern Africa's continental dunefields and isolated dunes, providing a rich record of aeolian system dynamics during the Late Quaternary. The majority of records come from sites within the five linear dune-dominated dunefields of the Kalahari, with lesser representation of other major dune areas, including the Namib and West Coast dunefields, and of other dune types, including lunettes and transverse forms. Dune database records are analysed not only in terms of the evidence they provide for Late Quaternary environmental changes over the last 190 ka, the purpose for which most ages have been produced, but in terms of the analytical techniques used, data quality and data presentation, as these all impact on how dune luminescence ages have been, or should be, interpreted as a tool for palaeoenvironmental and dune development studies.It is concluded that, even despite the number of dated dune records from southern Africa, there is a marked spatial unevenness within and between dunefields in the data available for assessing dune depositional ages and conditions. However, this is not a situation that can simply be improved upon by adding more and more ages to the full set of records. It is both necessary to appreciate the spatial differences in dune sensitivities to activation and relationships to potential changes in hydrological and other activity controls, and to establish better tools and approaches for analysing a rich but presently environmentally ambiguous record of dune accumulation.

Stratigraphic architecture of alluvial–aeolian systems developed on active karst terrains: An Early Pleistocene example from the Ebro Basin (NE Spain)

During the Early Pleistocene, fluvial, alluvial and aeolian depositional systems interacted in the central Ebro Basin, Spain, constructing wide alluvial plains over a Neogene evaporite substratum. Fluvial sediments, mainly longitudinal gravel bars and channels, are interdigitated with gravel mass flow and distal mudflat deposits. Aeolian sedimentation is registered as aeolian dunes and sand sheets. Episodes of fluvial deposition alternated with periods of alluvial fan progradation and aeolian deposition. These changes are related to climate-driven water availability. Stratigraphic units and deformation structures show synsedimentary karstification of the evaporite substratum that, although karst was not restricted to any particular climate scenario, was probably favoured during periods of high water availability. Karstification conditioned the development of local sedimentary depocentres which, in turn, influenced the distribution of sedimentary subenvironments as well as the accumulation and preservation of aeolian dunes and lacustrine–palustrine deposits. Stratigraphic architecture shows that thickening of the series due to karst subsidence did not occur homogeneously, but was controlled by diachronous subsidence resulting in numerous angular unconformities. In subsiding karst areas transport capacity was reduced and sediment preservation increased.

Análisis Fitolítico de la Formación Tezanos Pinto (Pleistoceno Tardío—Holoceno Temprano) en el Sector Sudoeste de la Provincia de Entre Ríos (Argentina)

Abstract. PHYTOLITH ANALYSIS OF TEZANOS PINTO FORMATION (LATE PLEISTOCENE-HOLOCENE) IN THE SOUTHWESTERN REGION OF ENTRE RIOS PROVINCE (ARGENTINA). Loess deposits are the main component of the Late Quaternary sequences of the Pampa plains (South America). The Last Glacial Maximum loess represents a depositional unit of the Pampean Aeolian System that evidences the expansion of semiarid conditions to the northeast of the region. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene—early Holocene of the northeastern Pampa region. Advances in the knowledge of the micropaleobotanical content of this geologic formation are presented in this work, especially the obtained results of the Southweastern area of Entre Rios Province. The analyzed phytolith assemblages show a high homogeneity with some variations that allowed their quantitative differentiation across the analyzed sedimentary profiles. The presence of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowe...

Design and Application of Aeolian Vibration Monitoring System for Overhead Transmission Line

Aim at the shortage of traditional Aeolian vibration fatigue tests and theoretical models for transmission line, the Aeolian vibration monitoring system of transmission line based on the ZigBee wireless network was designed. The system transfer real-time field data of meteorological factors, tension of conductor and acceleration of monitoring nodes to background computer. The line vibration curve integrated directly from the acceleration sensor recorded data will present a serious problem of baseline drift. Therefore, based on least-square theory, a new baseline correction method is proposed to eliminate effect on drifts, and then obtain distortion less vibration curve of transmission line by twice integrations. The system running results show that track fitted with monitoring data is in good agreement with the real recorded trajectory. The system can satisfy the needs of the real time monitoring on transmission line site and be well applied to the calculation of conductor fatigue damage.

Micro‐topographic analysis of shell pavements formed by aeolian transport in a wind tunnel simulation

Beach surfaces containing shell materials represent one end‐member of a range of environments in which armoring is the primary control on wind erosion. Unlike spheres and cylinders which have formed the basis of theoretical model formulation and much of the early work in wind tunnels, mollusc shells have complex and non‐uniform shapes which vary with their orientation. Identification of shell perimeter, height and frontal area relative to the bed area (roughness density) is therefore a formidable task, but nonetheless is essential for modeling sediment entrainment from beach surfaces. A methodology is suggested in this paper for capturing and analyzing these geospatial data, in the context of a wind tunnel simulation designed to improve understanding of the geophysical processes involved in armoring. For deposits where non‐erodible shells represent half of the volume of the parent material, the surface appears to be highly stable to wind erosion from the outset, although minor reworking of the intervening, erodible sediment does occur. In comparison, the shell coverage must increase to approximately 30% during wind erosion events in order for any given beach surface to stabilize, especially beach deposits with a low concentration of shells by volume. With suitable calibration, the Raupach shear stress partitioning model can be forced to perform well in predicting the threshold conditions for particle entrainment. However, this approach overlooks the pivotal involvement of particle impact and ricochet in the creation and sculpting of the armored bed. As a case in point, when the shells are removed from digital elevation models of armored beach surfaces formed in aeolian systems, the adjusted topography is not suggestive of the presence of coherent flow structures (e.g., horseshoe vortices and wedge shaped shelter areas) as assumed to exist in the stress partitioning approach for isolated flows. This would suggest that future work on the armoring of natural surfaces affected by wind erosion must allow for more complexity in the flow perturbation.

Dune field development, interactions and boundary conditions for crescentic and stellate megadunes of the Al Liwa Basin, the Empty Quarter

ABSTRACTWithin the greater Ar Rub' al Khali (Empty Quarter) sand sea lies an internal depocentre, the Al Liwa Basin, which comprises a variety of mega‐scale dune types. Crescentic dunes dominant the north of the basin while megadunes of stellate or star form are a major landform of the south‐eastern reaches. Their development into dune fields is determined by the style and rate of dune–dune interactions, the boundary conditions imposed by a multi‐modal wind regime, fluctuating groundwater levels, and sediment availability under an assortment of climatic conditions throughout the Quaternary. As a result, dune field patterns are a collective response to these perturbations in space, time and environment. The R‐statistic is a collective measure of these responses, and is a metric capable of identifying the degree of pattern maturity or self‐organization of the aeolian system, and the pathways from which patterns evolve. The spatial signature of the southerly located star dunes is characterized by two definitive patterns of organization: the first, one of complete spatial randomness, the second, a low degree of spatial uniformity. In isolation, these results appear to be unrelated to those for crescentic dunes of the region in which a significantly higher degree of pattern dispersion is the norm. However, when spatial statistical measures are integrated with the theoretical understanding of dune–dune interactions and the involvement of environmental agents, the complex morphodynamic pathways and linkages between regional dune fields is better understood. In this case, both constructive (e.g. merging, lateral linking) and regenerative activity (e.g. calving) have played important roles in the development of dune size, and associated adjustments in spacing, and dune numbers, and subsequently dune field patterns. Synergetic patterns are emblematic of this vast dunescape, whereby transitional geographic, morphologic, dimensional and environmental modifications exist between the mega‐crescentic and mega‐stellate dunes of the Empty Quarter. Copyright © 2012 John Wiley & Sons, Ltd.

Modeling CO2 saturation distribution in eolian systems

Eolian sandstone hydrocarbon-bearing reservoirs have been target of CO2 enhanced oil recovery as well as potential CO2 sequestration sites. These sandy reservoirs are compartmentalized by the presence of bounding surfaces, which can function as flow barriers. In this study, eolian packages of a specific outcrop are modeled and their bounding surfaces effects on multiphase flow in CO2 upward migration are simulated through adequate enforcement of capillary barriers in a compositional simulator. We investigate how two-scale dune foresets strike directions of the outcrop could hint on the choice of well direction to increase storage in this particular model. The genetic unit of eolian strata is small and therefore their corresponding heterogeneity features, such as bounding surfaces, require higher resolution than that available through well logs. We build a synthetic eolian simulation model with associated bounding surfaces, geometrically inspired by the Permian Cedar Mesa Sandstone in southern Utah, USA. Permeability values of sand bodies and bounding surfaces are taken from actual outcrop reported data and surface examples to produce a lower bound of absolute permeability contrast. Capillary pressure is parameterized by the gridblock permeability, which implies that the capillary pressure contrast also represents a lower bound on the basis of published information. Our results show that bounding surfaces markedly reduce accessibility ratio (sweep efficiency), up to 55%, compared with cases where bounding surfaces are ignored, resulting in a larger plume size beneath the caprock and also higher leakage risk. Interestingly, well direction with respect to foreset strike direction has negligible effects on trapping and accessibility ratio for the low inclination angle. The methodology developed in this study could be applied to study CO2 storage in other eolian formations.

Late Quaternary megafans, fans and fluvio-aeolian interactions in the Bolivian Chaco, Tropical South America

The Chaco is a huge plain and a main biogeographic biome of South America dominated by subtropical semi-deciduous vegetation that spreads on the Andes footslope on more than 800,000km2 through Bolivia, Argentina and Paraguay. The climate is tropical wet–dry and the South American Summer Monsoon (SASM) leads to intensive convective rainfall during the summer season. Some of the world's largest river–fans such as the Parapeti and Grande rivers megafans developed in the Bolivian Chaco. Our research was based on morpho-sedimentary information and sustained by 25 OSL dating of fluvial and aeolian sediments. We demonstrate that these megafans are bigger than previously postulated by some authors. Morphostratigraphic analysis, geochronological data and regional correlations suggest that the Chaco megafans and large piedmont fans were generated and reached maximum development during the middle pleniglacial and early pleniglacial (ca. 60 to 28ka) because of the presence of colder and more seasonal conditions (dry–wet intense contrasting seasons) than those existing today in the Amazon and the Bolivian plains. We suggest that a main mechanism triggering the megafan development was the presence of an intense monsoonal effect on the Eastern flank of the Andes that enhanced rainfall by orographic excitation during MIS 3 and the early part of MIS 2 that produced an increase in discharge and sediment supply. Concomitantly to fluvial processes the deflation of fluvial belts occurred and big sand dune fields developed by winds blowing out from North to South following the same pattern the South American lower level jet follows presently. Maximum aridity was reached during MIS 2 with the deposition of loess deposits on the piedmont areas and megafan surfaces, the continuous generation of aeolian dunes and a remarkable decrease in the fluvial activity. Cold air mass related to the polar advection (friagens or surazos) probably affected the area with more intensity and frequency. The Lateglacial was also arid but probably less extreme than the LGM. During a good part of the Holocene the climatic conditions were still arid to semiarid but became more similar to the present sub-humid climate since ~1.5ka. During the Holocene, the megafans and aeolian systems didn't reach Late Pleistocene size and level of activity.

Analyzing dune dynamics at the dune-field scale based on multi-temporal analysis of Landsat-TM images

Studying dune dynamics at the dune-field scale requires intensive fieldwork and a relatively huge dataset. However, this is not always possible with the high cost and the limited availability of data. Here, we present a technique based on the analysis of multi-temporal Landsat-TM images for studying the dynamics of different dune morphologies from five dune-field sites around the world. A pair of Landsat-TM images for each site has been used after performing several steps of image pre-processing and enhancement (i.e. image co-registration, radiometric calibration and histogram equalization). RGB-clustering is a commonly used algorithm for data compression and iso-clustering. In this study, we implemented this technique as an unconventional change-detection algorithm with 32 clustering partitions per band. A bi-temporal layerstack of the near-infrared bands was the input for the RGB-clustering process. RGB-clustering produced thematic maps that gave an immediate insight into the dune dynamics at the dune-field scale given the availability of Landsat images. The technique gave the best results with dunes developed under uni-directional wind pattern. In addition, it was also easier to detect migration of simple dunes than in compound or complex dunes. These maps can be used as a bi-temporal digital atlas of large dune-systems and help in defining areas for detailed field measurements on dune dynamics and migration. Moreover, it can be implemented in analyzing aeolian systems where field measurements are practically impossible (i.e. large and extra-terrestrial aeolian systems).

Paleoenvironment and paleontology of the Andapaico Formation (upper Paleozoic, central Precordillera, Argentina)

A sedimentological, paleontological and paleoenvironmental study of the Andapaico Formation is presented (southern sector of the Paganzo Basin, San Juan). This unit overlies with an angular unconformity the Punta Negra Formation, and has a thickness of 430 m of siliciclastic sediments, that include deposits formed predominantly in nearshore environments. Lower shoreface (facies association I), anastomosed rivers and floodplain (II), high sinuosity rivers (III), beach (IV), eolian system (V), barrier island (VI) and lagoon (VII) deposits were identified. Facies association I (lower part of the unit) and VII (upper part) and their associated palynoflora assign them to the early Cisuralian (I) and late Cisuralian-early Guadalupian (VII, Lueckisporites-Weylandites Biozone). From the facies I association a fossil plant assemblage was obtained that allows it to be referred to the Ferugliocladus Superzone of the early Permian of the Tepuel-Genoa Basin, which reinforces the hypothesis of this age for the lower part of the Andapaico Formation.

The aeolian system of central Argentina

Abstract The central region of Argentina comprises three main geomorphological domains, the Pampean plain, the northern Patagonia plateau and the eastern Andean piedmont. The region characterized by a complex morphostructural setting is covered by a late Quaternary aeolian apron with subordinate alluvial deposits, grading from loess and loess-like deposits in the eastern Pampas to sandy mantles and dunefields in the central, western and southern areas of the region. Eight aeolian units have been identified on the basis of the nature of the deposits, landforms and their geological-structural settings. Loess and loess-like mantles are the dominant aeolian facies of three units extending across the eastern Pampean plain: loess and loess-like mantles, loess and loess-like mantles and blowouts, sandy loess and loessial sand mantles. Dunefields and sand mantles prevail in five other units: central Pampean dunefields, western Pampean sand mantles and dunefields, western Pampean dunefields, Andean piedmont dunefields, northern Patagonia and southern Pampean sand mantles and dunefields. At a regional scale, sandy deposits are proximal facies closer to the main source area of aeolian material corresponding to the floodplain environment of the Colorado River and its tributary Desaguadero–Salado-Curaco fluvial system. The eastern loess deposits correspond to distal aeolian facies. In addition, topography governed by the complex subsurface geology and structure of the region, play a leading role as a primary controlling factor in the distribution of aeolian facies and the resulting landforms.

Constructing hydrocarbon reservoir analogues of aeolian systems using ground penetrating radar

Abstract This paper presents a three-dimensional ground penetrating radar (GPR) case study of contemporary dunes from southern Libya that may serve as an analogue for oil and gas reservoirs in aeolian systems. A 30 MHz inline GPR system was used to image an undulating region 260 m wide × 480 m long in less than 4 h, with a line spacing of approximately 1 m at survey speeds of over 30 km/h. The internal aeolian architecture was imaged to a depth of about 40 m. Complex three-dimensional cross-stratification is evident within the resultant 3D data cube. A full range of dune heterogeneity is inferred: facies interaction between lake and dune environments, the course of ancient streams, dune field/sand sheet relationships, bounding surface geometry and primary strata type distribution. Different dune generations are perceived within the survey, with complex superimposed relationships apparent. Near-surface sand sheet and deeper linear dune/barchanoid ridge geometries are revealed. However, it is recognised that the complex pattern of contemporary dune formations in the area may indicate alternative interpretations. Finally, the distribution of appropriate reservoir properties is discussed.

A stratigraphic model to account for complexity in aeolian dune and interdune successions

AbstractWet aeolian systems, in which the water table or its capillary fringe are in contact with the accumulation surface, such that moisture influences sedimentation, are well‐known from modern aeolian systems and several ancient preserved successions are recognized from outcrop. One common mechanism by which accumulation of wet aeolian system deposits occurs is via a progressive rise in the relative water‐table level that is coincident with ongoing dune and interdune migration, the angle of dune climb being determined by the ratio between the rate of relative water‐table rise and the rate of downwind migration of the bedforms. Accumulations of wet aeolian system deposits tend to be characterized by units of climbing dune strata separated by units of damp or wet interdune strata. For simple geometric configurations, where the size of the dune and interdune units, the rate of bedform migration and the rate of aggradation all remain constant over space and time, the resulting accumulation has a simple architecture characterized by sets of uniform thickness inclined at a constant angle. However, the dynamic nature of most aeolian dune systems means that such simple configurations are unlikely in nature. The complexity inherent in these systems is accounted for here by a numerical model in which key controlling parameters, including dune and interdune wavelength and spacing, migration rate and aggradation rate, are allowed to vary systematically both spatially (from a dune‐field centre to its margin) and temporally (in response to changes in sediment availability or water‐table level). The range of synthetic stratigraphic architectures generated by the model accounts for all the best‐known examples of aeolian dune and interdune stratigraphic configurations documented from the stratigraphic record. Modelling results have enabled the erection of a scheme for the classification of dune system type whereby the many elaborate stratal architectures known to exist in nature can effectively be accounted for by only four parameters that are allowed to vary over space and time: dune and interdune wavelength and spacing, rate of bedform migration and rate of accumulation. Results have applied implications, including the modelling of reservoir heterogeneity and the prediction of fluid flow pathways of hydrocarbons, water, CO2 and contaminants in subsurface reservoirs and aquifers, in which low permeability interdune units might act as baffles or barriers.

Orbital observations of contemporary dune activity in Endeavor crater, Meridiani Planum, Mars

[1] Although aeolian landforms are pervasive on Mars, evidence for contemporary activity has been limited. The next major campaign for the Mars Exploration Rover “Opportunity” is the investigation of the ∼20 km diameter Endeavor crater, ∼6 km to southeast of the rover's position as of December 2010. We present evidence from orbital imagery that eight aeolian bed forms (∼14,000 m2) in Endeavor crater have been active within the past decade (2001–2009), at a spatial scale that should be directly observable by Opportunity from the crater rim. Two dunes appear to show translational migration (∼10–20 m), but all dunes indicate erosion to be the dominant process with up to 100% sediment removal. Thermophysical properties of these dunes are consistent with very fine to fine sand sizes, the particle sizes most easily moved by the Martian atmosphere. The dunes that show the most surface change have a rippled appearance without well-defined slip faces. Based on their morphology (elliptical shape), we classify them as dome dunes. Mesoscale atmospheric modeling is employed to provide insight into the atmospheric forcing of this aeolian system. The major wind regimes from modeling are consistent with observations of wind streaks, sand streamers, ripples, and slip faces of regional dune fields although modeled wind speeds are insufficient to move sand. The translation and erosion of these dunes constitutes the largest contemporary movement of sand-sized sediment reported on Mars to date and demonstrates that Endeavor crater has been subject to wind profiles exceeding the threshold velocity at the surface (daily/seasonally and/or episodically) in the recent past.

Aeolian scours as putative signatures of wind erosion and sediment transport direction on Mars

Obstacle marks, specifically current crescents (scours) formed by aeolian erosion, have not been previously identified on Mars from orbit. However, recent Mars Reconnaissance Orbiter images of an unnamed intracrater dune field within the Hellespontus region have shown innumerable meter-scale scours around fine and medium grade blocks. The types, relative numbers, and distributions of scour features served to determine, by proxy, the modes of surface wind direction and pathways of sediment transport across the crater floor. The orientations of scours of U-type morphology as well as the facing directions of leeward slopes for crescentic dunes (barchans and barchanoids) and megaripples were examined by statistical methods to determine their reference directions and dispersion of modal classes. We showed that although the dune field has evolved primarily under the influence of winds from the southwest, U-type scours have developed predominantly from a significant northwesterly wind direction. These data suggest that the dune field has evolved under the influence of a bimodal wind regime. Furthermore, such an aeolian system may help to explain the intermediary morphology between crescentic and linear for the central part of the dune field, in which the dunes appear to have undergone longitudinal as well as lateral sediment transport. In the absence of direct measurements of wind directions and strengths, current crescents offer detailed data from which planetary air flow at the surface–air interface can be better interpreted for the many intracrater settings across Mars.

Transgressive dune formation along a cliffed coast at 75 ka in Sardinia, Western Mediterranean: a record of sea-level fall and increased windiness

Transgressive dunes develop frequently along strandplain coastlines; however, they may also form along rocky coasts dominated by cliffs and embayments. Two lithified transgressive dune systems developed along the cliffed Alghero coast (NW Sardinia, Italy) have been investigated. One aeolian system forms a cliff-front anchored aeolian dune accumulation; the other is a valley-head anchored sand-ramp system. Optically stimulated luminescence ages indicate that both systems formed around 75 ka. This period, which corresponds to the beginning of MIS 4, was characterized by a relatively low sea-level stand (15 m below the present sea level) and was preceded by a sea-level highstand (+1 m asl) around 81 ka (MIS 5a). Our results show that this rapid sea-level fall exposed an enormous amount of marine sand, which was transported inland by strong northerly winds and deposited in front of cliffs or in valley heads. Therefore, sediment supply and sea-level fall seem to be critical factors controlling dune formation along rocky coasts, which generate time-transgressive aeolianites. Terra Nova, 00, 000–000, 2010

Life history and captive rearing of the Wekiu bug (Nysius wekiuicola, Lygaeidae), an alpine carnivore endemic to the Mauna Kea volcano of Hawaii

The hemipteran family Lygaeidae contains species that are overwhelmingly plant and seed feeders. The Wekiu bug, Nysius wekiuicola, a candidate endangered species endemic to the summit of the 4,205 m volcano, Mauna Kea, and the closely related A’A bug, Nysius aa, are the only obligate carnivore scavengers of the family. Despite its unique diet, remarkable ecology, and high profile due to conservation concerns, there is still little known about the Wekiu bug. We present the first detailed observations and descriptions of the Wekiu bug, including a complete life history. The Wekiu bug lays eggs singly or in small loose clutches, matures after five nymphal instars, and can survive and reproduce at constant temperatures never found in its natural habitat. Our results clearly demonstrate the importance of behaviour, rather than pure physiological adaption, in an insect’s persistence in a harsh environment. The Wekiu bug’s shift to carnivory from a suite of herbivorous congeners is a remarkable adaptive shift in an aeolian system bereft of vascular plants. Finally, we relate the specialized life history of the Wekiu bug to its conservation on the arid, frigid summit of the Mauna Kea volcano. This unique habitat is increasingly impacted by tourism and telescope facilities.

Understanding linear dune chronologies: Insights from a simple accumulation model

Dunefields are today often found in regions where environmental conditions are no longer conducive to widespread aeolian transport and deposition, and are thus seen as potential archives of palaeoenvironmental information. Some dune types are more suitable for this purpose than others, and linear dunes (used here synonymously with longitudinal dunes) have been most frequently employed. They are commonly found in dryland and dryland-marginal regions, and they are apparently less migratory than some other dune forms, thereby offering the potential for longer environmental histories. Most recent studies have employed optical (OSL) dating surveys, which directly date the emplacement of dune sands, to attempt to produce a representative history of aeolian accumulation at a dunefield scale; yet such studies have not always given due consideration to the geomorphology of linear dune accumulation. Although linear dunes do not rework their sand as readily as, say, barchans dunes, it is clear that sand deposited during an aeolian event is likely to have been removed from elsewhere on the dunefield's surface. For this reason, all dune archives must be assumed to be discontinuous over long timescales. The effect of sediment redistribution on dune preservation, and thus palaeoenvironmental interpretation, is difficult to observe and poorly understood. We present a simplified probabilistic model to replicate deposition/erosion of sand at a linear dune crest, thus simulating the type of profile sampled in many field studies in order to produce a local accumulation history. The modelled sand flux incorporates various feedbacks and the simulations are run with varying boundary conditions in which the simulated surface is assumed to be in equilibrium over the multi-millennial timescales of the model's duration. Periodic instabilities in the landscape are generally well recorded by the modelled dune accumulation history, particularly when the events involve the system as a whole briefly functioning out of an equilibrium state (i.e. the probabilities of deposition and reworking are not equal). However, under forcing conditions where the probabilities are unchanged throughout the duration of the model run, the results can show apparent structure within the data when sample sizes are low, although at large sample sizes the preservation potential decays with burial age according to a power law. The model confirms the importance of rigorous sampling strategies for such studies, but also suggests that if such precautions are taken, the reworking inherent to linear dune aeolian systems does not preclude their use as a Quaternary palaeoenvironmental archive of environmental change.

Nearest neighbor analysis of mega-barchanoid dunes, Ar Rub' al Khali, sand sea: The application of geographical indices to the understanding of dune field self-organization, maturity and environmental change

The geographic signature of dune distribution and self-organization as measured by the R-statistic offers a viewpoint on the geography of crescentic aeolian systems and proposes an index from which to determine the degree of self-organization (maturity) and possibly relative age, across a variety of spatial scales and planetary contexts. This analogue study examines and compares the geography of crescentic megadune patterns for the Al Liwa basin of the Ar Rub' al Khali sand sea on the Arabian Peninsula. Fields of mega-barchanoid forms have shown the degree of self-organization to be largely an association between morphological diversity and dimensional variability. In short, fields of transitional megadunes (barchanoid-seif) are comparatively less regular in distribution than are those fields, or part thereof, that consist of ubiquitous compound (barchanoid) morphologies whose patterns are more highly regular. The change in dune morphology, dimensions and spatial signature can, for the most part, be associated with the directional differences and varying intensities of the north-westerly Shamal and reversing south-westerly Kharif wind regimes. Such associations have significant bearing on the maturity of dunefields and their response to sediment supply, transport capacity and sediment availability within an aeolian system. This study provides an analogue on which to base further comparative studies with other terrestrial dune fields, as well as the ergs and intracrater fields of Mars.